Semimetal/Substrate Cavities Enabling Industrial Materials for Structural Coloring

Color coatings are essential for the identification and safety of everyday objects as well as for the protection of surfaces from deterioration, in addition to their well-known use for enhancing their aesthetic appeal. However, conventional dyes and pigments are a major source of contamination and degrade easily over time. Structural coloring is a sustainable alternative capable of producing high-quality colors with nanometric structures. Nonetheless, many approaches to structural coloring rely on lithography or expensive back-reflectors made from noble metals. In this study, we approach surface coloring using lightweight, sustainable, and scalable optical coatings with subwavelength thickness. This method allows industrial surfaces to function as active elements in the color-generating structure, eliminating the need for metallic mirrors. The design is based on a semimetal/substrate cavity (SSC), directly deposited onto the surface to be colored. As a proof of concept, we designed and fabricated SSCs on silicon and stainless steel substrates, using ultrathin films of bismuth (Bi) and aluminum oxide (Al₂O₃) as the cavity components. These SSCs display vivid, well-defined colors with excellent angular stability for a cavity. Moreover, the SSC design can be adapted with other semimetal/dielectric combinations and offers an efficient, daylight-friendly, sustainable, and lightweight solution for functional coloration of everyday objects as well as components for industrial and technical applications.